# year    value 
 1901 6.327061 
 1902 6.513813 
 1903 6.834598 
 1904 7.313065 
 1905 6.662226 
 1906 6.719322 
 1907 6.684418 
 1908 6.379711 
 1909 6.220875 
 1910  6.86008 
 1911 7.480486 
 1912 6.543288 
 1913  6.90326 
 1914 6.618059 
 1915 6.666636 
 1916 7.235643 
 1917 6.339262 
 1918 6.973125 
 1919 6.391085 
 1920 7.623953 
 1921 7.644689 
 1922 6.452347 
 1923 7.304589 
 1924 6.655784 
 1925  6.80499 
 1926 7.535911 
 1927 7.379337 
 1928 7.514395 
 1929 6.752463 
 1930 7.555371 
 1931 6.490951 
 1932 6.949056 
 1933 6.333572 
 1934 7.836956 
 1935 6.937031 
 1936 7.233976 
 1937 7.349428 
 1938 7.041826 
 1939 6.925586 
 1940 5.858858 
 1941 6.180095 
 1942 6.860805 
 1943 7.910846 
 1944 6.827323 
 1945 7.667742 
 1946 7.555206 
 1947 7.840213 
 1948 7.673755 
 1949 7.840849 
 1950 7.868509 
 1951 7.688321 
 1952 7.253732 
 1953 7.486724 
 1954 6.631066 
 1955 6.955416 
 1956 6.216107 
 1957 7.403139 
 1958 7.482094 
 1959 7.738118 
 1960 7.297237 
 1961 8.051739 
 1962  6.56324 
 1963 6.579655 
 1964 7.240923 
 1965 6.570185 
 1966 7.512191 
 1967  7.45451 
 1968 7.105605 
 1969 6.820075 
 1970 6.870771 
 1971 7.178492 
 1972 7.019005 
 1973 7.024437 
 1974 7.470156 
 1975 7.483697 
 1976  7.15125 
 1977  7.46566 
 1978 6.595509 
 1979 7.218921 
 1980 6.552144 
 1981 7.182643 
 1982 7.814019 
 1983 7.756811 
 1984 6.872021 
 1985 6.923011 
 1986 7.258727 
 1987 7.113452 
 1988 7.853188 
 1989 7.987933 
 1990   8.1476 
 1991 7.292819 
 1992 8.114198 
 1993  7.66535 
 1994 8.813594 
 1995 7.758123 
 1996 7.073145 
 1997 8.111614 
 1998 8.030347 
 1999 8.086094 
 2000 8.721308 
 2001 8.043513 
 2002 8.615994 
 2003 8.378711 
 2004 7.861689 
 2005 7.524736 
 2006 8.333976 
 2007 8.647461 
 2008  8.38001 
 2009 8.462286 
 2010 7.458574 
 2011 8.852525 
 2012  8.50233 
 2013 8.127648 
 2014 9.208764 
 2015 9.099698 
 2016 8.673236 
 2017 8.665361 
 2018 9.402266